1. Field of the Invention
The present invention relates to X-ray sensing devices and to liquid crystal display (LCD) devices. More particularly, it relates to a method of fabricating thin film transistor (TFT) array substrates for use in X-ray sensing devices and in LCD devices.
2. Description of Related Art
X-ray sensing devices (referred to as X-ray detectors hereinafter) and liquid crystal display (LCD) devices include thin film transistors (TFTs) as switching elements. The X-ray detectors act as sensing devices and the LCD devices act as displaying devices.
Since the X-ray detectors employ TFTs, the X-ray detectors have the advantage of providing real time diagnosis. Operating principles and configurations of the X-ray detectors are explained hereinafter.
FIG. 1 is a cross-sectional view illustrating one pixel of an array substrate of a related art X-ray detector. That X-ray detector includes a thin film transistor (TFT) “T” on a substrate 1, a photoconductive film 2, and various conductive elements that are described subsequently. Also included, but not shown in FIG. 1, are a scanning integrated circuit and a data integrated circuit.
Still referring to FIG. 1, the photoconductive film 2 produces electron-hole pairs 6 in proportion to the strength of incident radiation, such as X-rays. Thus, the photoconductive film 2 acts as a photoelectric transducer that converts incident X-rays into electron-hole pairs 6. An external voltage Ev is applied across a conductive electrode 7 to a pixel electrode 8. That voltage causes the electron-hole pairs 6 in the photoconductive film 2 to separate such that X-ray induced electrical charges accumulate on the pixel electrode 8. Those electrical charges are applied to a second capacitor electrode 13, and are consequently stored in a storage capacitor “S” formed by the second capacitor electrode 13 and a first capacitor electrode 11 that is formed over a ground line 9. The pixel electrode 8, the first capacitor electrode 11 and the second capacitor electrode 13 are beneficially comprised of a transparent conductive material such as Indium-Tin-Oxide (ITO). Furthermore, an insulating dielectric layer 15 is interposed between the first capacitor electrode 11 and the second electrode 13. That dielectric layer is beneficially comprised of Silicon Nitride (SiNx).
When forming the first capacitor electrode 11, the transparent conductive material such as ITO is deposited and patterned at a temperature of 210 degrees Celsius. However, when forming the insulating dielectric layer 15, the deposition and patterning processes are performed, at a temperature of 250 degrees Celsius. Therefore, during the process of forming the insulating dielectric layer 15 after forming the first capacitor electrode 11, the higher temperature (250 degrees Celsius) affects a surface of the first capacitor electrode 11, and thus contact defects between the first capacitor electrode 11 and the insulating dielectric layer 15 occur. Namely, a gap or a space is formed in the interface where the first capacitor electrode 11 and the insulating dielectric layer 15 contact each other.
The problem described above also occurs in an array substrate for use in an LCD device. FIG. 2 is a cross-sectional view illustrating one pixel of a related art LCD device. As shown, the LCD device 21 has lower and upper substrates 25 and 29 and an interposed liquid crystal layer 31. The lower substrate 25 has the TFT “T” as a switching element to change an orientation of the liquid crystal molecules and includes a pixel electrode 23 to apply a voltage to the liquid crystal layer 31 according to signals of the TFT “T”. And, a protective insulation layer 33 is formed on the pixel electrode 23 and on the TFT “T” to protect the pixel electrode 23 and the TFT “T”. The upper substrate 29 has a common electrode 27 thereon. The common electrode 27 serves as an electrode for applying a voltage to the liquid crystal layer 31.
Still referring to FIG. 2, the pixel electrode 23 contacts the drain electrode of the TFT “T” and applies a signal received therefrom to the liquid crystal layer 31. Thus, the signal re-arranges the liquid crystal molecules into a determined pattern due to a spontaneous polarization in accordance with the applied signal. The LCD device displays images, due to the fact that the transmittance of light generated from a backlight device (not shown) is controlled by the re-arrangement of the liquid crystal molecules. Meanwhile, the pixel electrode 23 is formed of ITO as in the case of the X-ray detector described above, and the protective insulation layer 33 is formed of silicon nitride (SiNx).
In the above-mentioned LCD device, during the process of forming the protective insulation layer after forming the pixel electrode, the higher temperature (250 degrees Celsius) affects the surface of the pixel electrode, and thus contact defects between the pixel electrode and the protective insulation layer occur. Namely, a gap or a space, as described in the case of the X-ray detector, is formed in the interface where the pixel electrode and the protection layer touch each other. These gaps or spaces decrease the manufacturing yield and throughput.